1. Field of the Invention
This invention relates to novel end-functionalized poly(vinyl ethers). More particularly, this invention relates to novel poly(vinyl ether) aminocarbamates and their use in fuel compositions to prevent and control engine deposits.
2. Description of the Related Art
It is well known that automobile engines tend to form deposits on the surface of engine components, such as carburetor ports, throttle bodies, fuel injectors, intake ports and intake valves, due to the oxidation and polymerization of hydrocarbon fuel. These deposits, even when present in relatively minor amounts, often cause noticeable driveability problems, such as stalling and poor acceleration. Moreover, engine deposits can significantly increase an automobile's fuel consumption and production of exhaust pollutants. Therefore, the development of effective fuel detergents or "deposit control" additives to prevent or control such deposits is of considerable importance and numerous such materials are known in the art.
Deposit control additives, however, differ in their effectiveness for preventing or controlling deposits on various engine components. This is believed to be due primarily to the fact that each engine component has a different operating temperature and some deposit control additives are not sufficiently stable on the surface of certain engine components to perform their intended function. In this regard, deposits on intake valves are particularly difficult to control, since intake valve operating temperatures can exceed 3000C. At such high temperatures, many fuel additives are too volatile to be effective, while others thermally decompose.
Therefore, it would be particularly desirable to provide effective deposit control additives which have improved thermal stability at normal engine intake valve operating temperatures and which further have a sufficient molecular weight so as to be nonvolatile at such temperatures. The present invention discloses a new class of poly(vinyl ether) aminocarbamate fuel additives having such properties.
Polyether fuel additives are well known in the art. These polyether additives, however, have a poly(oxyalkylene) "backbone", i.e. the polyether portion of the molecule consists of repeating oxyalkylene units, i.e. [--CHR--CHR--O--].sub.x. In contrast, the fuel additives of the present invention have a vinyl ether polymer backbone consisting of repeating vinyl ether units, i.e. [--CHR--CR(OR)--].sub.x.
U.S. Pat. No. 4,191,537, issued Mar. 4, 1980 to R. A. Lewis et al., for example, discloses a fuel composition comprising a major portion of hydrocarbons boiling in the gasoline range and from 30 to 2000 ppm of a hydrocarbyl poly(oxyalkylene) aminocarbamate having a molecular weight from about 600 to 10,000, and at least one basic nitrogen atom. The hydrocarbyl poly(oxyalkylene) moiety is composed of oxyalkylene units selected from 2 to 5 carbon oxyalkylene units. These fuel compositions are taught to maintain the cleanliness of intake systems without contributing to combustion chamber deposits.
Similar hydrocarbyl poly(oxyalkylene) aminocarbamates and fuel compositions containing such additives are described in U.S. Pat. Nos. 4,160,648; 4,197,409; 4,236,020; 4,270,930; 4,274,837; 4,288,612; 4,778,481; 4,881,945; 5,055,607; and in PCT International Patent Application Publication No. WO 90/07564, published Jul. 12, 1990. The aminocarbamates described in each of the aforementioned patents have a poly(oxyalkylene) backbone.
End-functionalized poly(vinyl ethers) are also known in the art. For example, A. Verma et al. in Polymer Preprints, 1991, 32, 322, describe the synthesis and characterization of functionalized poly(butyl vinyl ether) oligomers having an aldehyde or a primary hydroxyl endgroup. These is poly(vinyl ethers) are prepared by the living polymerization of butyl vinyl ether using a hydrogen iodide/zinc iodide initiating system. The polymerization reaction is terminated with aqueous potassium carbonate to form the aldehyde endgroup, which can subsequently be reduced to form the primary hydroxyl endgroup.
Poly(vinyl ethers) having amine end-groups are also known. C. G. Cho et al., Polymer Preprints, 1987, 28, 356, describe the synthesis of amine-terminated poly(alkyl vinyl ethers) by quenching the living polymerization of alkyl vinyl ethers with p-methyl styrene and an amine. The resulting poly(alkyl vinyl ether) is covalently linked to the amine through a p-methyl styrenic unit.
M. Miyamoto et al., Macromolecules, 1985, 18, 123, describe the synthesis of poly(vinyl ethers) having a terminal amine group by quenching the living polymerization reaction of vinyl ether monomers with aliphatic amines. The resulting poly(vinyl ether) amines have an .alpha.-amino ether endgroup.
Similarly, M. Sawamoto et al., Polymer Bulletin, 1987, 18, 117, describes quenching vinyl ether polymerization reactions with anilines to form aniline-terminated poly(vinyl ethers).
Amine-terminated poly(isobutyl vinyl ethers) having a primary amine at the beginning of the vinyl ether polymer are described by T. Hashimoto et al. in J. Poly. Sci. Polym. Chem. Ed., 1990, 28, 1137. These poly(vinyl ethers) are prepared by initiating the living polymerization of isobutyl vinyl ether with 2-(vinyloxy)ethyl phthalimide. The phthalimide group is then removed with hydrazine to produce a poly(isobutyl vinyl ether) having a 2-aminoethyl ether moiety on the first vinyl ether unit of the polymer.
It has now been discovered that the thermal stability of polyether fuel additives can be substantially improved by is replacing the poly(oxyalkylene) component of such additives with a poly(vinyl ether) component. The resulting poly(vinyl ether) aminocarbamates are surprisingly effective for controlling fuel system deposits, particularly intake valve deposits.